1. Field of the Invention
The present invention relates in general to exhaust manifolds for an automotive internal combustion engine, and more particularly to exhaust manifolds of a type which is simple in construction and exhibits excellent performance against a thermal stress applied thereto.
2. Description of the Prior Art
The exhaust manifold is connected to a cylinder head of an internal combustion engine to carry combusted gases away from the piston chambers of the engine. As is known, since the combusted gases from the piston chambers have very a high temperature, the exhaust manifold is constructed to have a considerable resistance against a thermal stress applied thereto by the gases. Furthermore, for unrestricted flow of the combusted gases from the piston chambers, the manifold is constructed to reduce a back pressure produced therein.
Thus, hitherto, various attempts have been taken for improving these performances.
Two of the exhaust manifolds hitherto proposed are disclosed respectively in FIGS. 4 and 5 of the accompanying drawings, which are described in Japanese Utility Model First Provisional Publication No. 59-148417.
The conventional exhaust manifold shown in FIG. 4 is of a type which is designed for a four-cylinder type internal combustion engine. The exhaust manifold has thus four branch tubes 41a, 41b, 41c and 41d, each having one end mated with an aperture formed in a steel flange member 42 and the other end mated with an aperture formed in a gas gathering tubular portion 43. The mated portions are welded. The flange member 42 is bolted to a cylinder head 44 of the engine in such a manner that the apertures of the flange member 42 are respectively mated with exhaust ports 45 formed in the cylinder head 44 of the engine. An outlet portion of the gas gathering tubular portion 43 has another flange member 46 welded thereto. For this connection, the flange member 46 has an aperture 46a into which the outlet portion of the tubular portion 43 is inserted. Thus, under operation of the engine, the combusted high temperature gases in the piston chambers are led through the exhaust ports 45 and the branch tubes 41a, 41b, 41c and 41d into the gas gathering tubular portion 43 and discharged therefrom through the outlet portion thereof.
The exhaust manifold shown in FIG. 5 is of a dual-manifold type and has four branch tubes 51a, 51b, 51c and 51d, each having one end mated with an aperture formed in a steel flange member 52 and welded thereto. The flange member 52 is bolted to a cylinder head 56 of an engine in such a manner that the apertures of the flange member 52 are respectively mated with exhaust ports 57 formed in the cylinder head 56 of the engine. The branch tubes 51b and 51c are joined at their outlet portions and welded to a first gas gathering tube 53a, while the branch tubes 51a and 51d are joined at their outlet portions and welded to a second gas gathering tube 53b. The outlet portions of the gas gathering tubes invention to provide an improved exhaust manifold which is free of the above-mentioned drawbacks.
According to the present invention, there is provided an exhaust manifold for a multicylinder type internal combustion engine. The exhaust manifold comprises a plurality of branch tubes each having one end adapted to connect with an exhaust port of the engine; a gas gathering tubular member having the branch tubes connected thereto thereby to lead the exhaust gases produced by the engine thereinto through said branch tubes; and an outlet tube connected to the gas gathering tubular member to discharge the gases therefrom, wherein at least two of the branch tubes are integral with the gas gathering tubular member.